The present invention relates to a digital copier with or without a facsimile function and a digital copier having a color image forming function and, more particularly, to a copier having a security function for keeping a record of images copied, transmitted and received so as to control data.
The leak of secret documents brought about by the spread of copiers is a social problem awaiting a solution. At the present stage of development, it is extremely difficult to determine by whom, when and by which copier documents were copied. Some advanced color copiers are capable of printing a yellow code mark of neutral tint on a paper together with the duplication of a document image. With this kind of copier, it is possible to identify the machine used to copy the document by decoding the code.
However, a neutral tint is not available with a black-and-white copier. Moreover, even the copier capable of outputting a code mark on a sheet does not allow the person who copied a document to be identified. In addition, once the copy is carried away, which document was copied without permission cannot be determined. The copier may be so constructed as to produce two copies from each document and leave one of them within the copier while outputting the other copy. This, however, aggravates the wasteful consumption of papers.
Facsimile apparatuses include one having a memory for storing the number of documents sent, addressee, addresser, and other supervisory information. However, even with this kind of facsimile apparatus, it is not practicable to identify the person sent the documents or the contents of the documents.